Organic light emitting device having an optical distance of a micro cavity and method of fabricating the same

ABSTRACT

An organic light emitting device can include a first electrode and a second electrode, and a red emission layer, a green emission layer and a blue emission layer which are positioned between the first electrode and the second electrode. Each of the red emission layer, the green emission layer and the blue emission layer can be disposed in an entirety of a red sub-pixel area, a green sub-pixel area and a blue sub-pixel area. A distance between the first electrode and the second electrode in at least one of the red sub-pixel area, the green sub-pixel area and the blue sub-pixel area can be a first-order optical distance equal to λ/2n, where λ is a wavelength of light emitted from each of the sub-pixel areas, and n is an average refractive index of a plurality of organic material layers disposed between the first electrode and the second electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Patent Application No.10-2014-0150304 filed on Oct. 31, 2014, in the Republic of Korea, thedisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

Embodiments of the present invention relate to an organic light emittingdevice and, more particularly, to an organic light emitting devicecapable of simplifying a manufacturing process, enhancing efficiency andreducing power consumption, and a method of fabricating the same.

Description of the Related Art

An organic light emitting diode (OLED) display is a self-luminousdisplay employing an organic light emitting device. The organic lightemitting device has an emission layer between an a cathode serving as anelectron injection electrode and an anode serving as a hole injectionelectrode. The organic light emitting device receives electrons from thecathode and holes from the anode and injects the electrons and the holesinto the emission layer. The injected electrons are combined with theinjected holes to form excitons. The organic light emitting device emitslight when the excitons transit from an excited state to a ground state.

OLED displays are classified into a top emission type, a bottom emissiontype, and a dual emission type according to emission directions of lightfrom the OLEDs, and are also classified into a passive matrix type andan active matrix type according to manners in which the OLEDs aredriven.

Contrary to the liquid crystal display (LCD), the OLED display requiresno separate light source. Accordingly, a lightweight and thin OLEDdisplay can be fabricated. The OLED display is advantageous in terms ofpower consumption since the OLED display requires a low driving voltage.Moreover, the OLED display exhibits excellence in color expressions,response time, viewing angle and contrast ratio (CR). For these reasons,the OLED display is under research as a next generation display.

With development towards higher-definition displays, the number ofpixels per unit area has increased, and higher brightness has beendemanded. However, the OLED display has a limit on current (A) per unitarea due to the emission structure of the OLED display. In addition,increasing the current applied to the organic light emitting deviceleads to lower reliability and increased power consumption of theorganic light emitting device.

FIG. 1 is a view schematically illustrating the structure of an organiclight emitting device 100 of the related art.

Referring to FIG. 1, the organic light emitting device 100 of therelated art includes a first electrode 110 (anode) formed on a substrateon which a red sub-pixel area Rp, a green sub-pixel area Gp and a bluesub-pixel area Bp are defined, a hole injection layer (HIL) 115, acommon hole transporting layer (common HTL) 120, a first holetransporting layer 125 (R-HTL), a second hole transporting layer 130(G-HTL), organic emission layers including a red emission layer (redEML) 135, a green emission layer (green EML) 140 and a blue emissionlayer (blue EML) 145, an electron transporting layer (ETL) 150, a secondelectrode 155 (cathode), and a capping layer (CPL) 160.

As shown in FIG. 1, for the organic light emitting device 100, the redEML 135, the green EML 140 and the blue EML 145 are patterned on the redsub-pixel area Rp, the green sub-pixel area Gp and the blue sub-pixelarea Bp respectively using a fine metal mask (FMM). As the organicemission layers are formed using the FMM as above, the fabricationprocess of the organic light emitting device becomes complex andproductivity of the organic light emitting device is lowered.

In addition, emission efficiency of the organic light emitting device100 may be improved by adjusting thicknesses of the first and secondhole transporting layer 125 and 130 and the organic emission layers 135,140 and 145 in the respective sub-pixel areas to produce a micro cavityeffect. However, since a structure having a second-order opticaldistance is applied to all of the red sub-pixel area Rp, the greensub-pixel area Gp and the blue sub-pixel area Bp, the red EML 135 in thered sub-pixel area Rp becomes thicker than the green EML 140 in thegreen sub-pixel area Gp and the blue EML 145 in the blue sub-pixel areaBp.

Due to the thickness of the red EML 135 of the red sub-pixel area Rpformed as above, the driving voltage of the organic light emittingdevice 100 significantly increases along with an increase in powerconsumption.

Further, as the red EML 135 becomes relatively thick, an opening of amask is clogged by organic material in the deposition process of thethick organic emission layer. This phenomenon is called mask rib. Themask rib leads to a poor organic light emitting device.

Accordingly, it is needed to overcome technological limitations onemission efficiency, lifetime and power consumption that deteriorate thequality and productivity of the OLED display. Currently, research isbeing widely conducted to develop an organic light emitting device whichis capable of enhancing emission efficiency, lifetime of the organicemission layer and viewing angle while maintaining the color gamut.

SUMMARY OF THE INVENTION

Various structures of an organic light emitting device for enhancingefficiency and lifetime of the organic light emitting device andreducing power consumption of the organic light emitting device havebeen proposed to improve quality and productivity of an OLED display.

Embodiments of the present invention propose an organic light emittingdevice structure capable of simplifying a process, enhancing efficiencyand reducing power consumption.

In view of the above, an object of the present invention is to providean organic light emitting device capable of simplifying a process byreducing the number of FMMs used in forming organic emission layers onthe organic light emitting device and a method of fabricating the same.

Another object of the present invention is to provide an organic lightemitting device capable of improving emission efficiency by applying astructure having a first-order optical distance to at least one of a redsub-pixel area Rp, a green sub-pixel area Gp and a blue sub-pixel areaBp of the organic light emitting device and a method of fabricating thesame.

Another object of the present invention is to provide an organic lightemitting device capable of reducing power consumption by lowering thedriving voltage and a method of fabricating the same.

It should be noted that objects of the present invention are not limitedto the above-described objects, and other objects of the presentinvention will be apparent to those skilled in the art from thefollowing descriptions.

Embodiments described herein provide an organic light emitting devicecapable of simplifying a manufacturing process, enhancing efficiency andreducing power consumption, and a method of fabricating the same.

In an embodiment of the present invention, an organic light emittingdevice includes a first electrode and a second electrode, and a redemission layer, a green emission layer and a blue emission layerpositioned between the first electrode and the second electrode, whereineach of the red emission layer, the green emission layer and the blueemission layer is disposed in an entirety of a red sub-pixel area, agreen sub-pixel area and a blue sub-pixel area, wherein a distancebetween the first electrode and the second electrode in at least one ofthe red sub-pixel area, the green sub-pixel area and the blue sub-pixelarea is λ/2n, wherein λ is a wavelength of light emitted from each ofthe sub-pixel areas, and n is an average refractive index of a pluralityof organic material layers positioned between the first electrode andthe second electrode in each of the sub-pixel areas.

The green emission layer may be disposed on the red emission layer, andthe blue emission layer may be disposed on the green emission layer incorrespondence with each of the sub-pixel areas.

A red light may emit in the red sub-pixel area, a green light may emitin the green sub-pixel area and a blue light may emit in the bluesub-pixel area.

The organic light emitting device may further include a holetransporting layer corresponding to an entirety of the red sub-pixelarea, green sub-pixel area and blue sub-pixel area and positioned belowthe red emission layer, the green emission layer and the blue emissionlayer, wherein a thickness of the hole transporting layer may be equalto or less than 1200 Å.

The distance between the first electrode and the second electrode in thered sub-pixel area may be λ/2n, wherein λ may be the wavelength of lightemitted from the red sub-pixel area, and n may be the average refractiveindex of the plurality of organic material layers disposed between thefirst electrode and the second electrode in the red sub-pixel area.

A first hole transporting layer may be positioned on the red emissionlayer in the green sub-pixel area.

The first hole transporting layer may include at least one of anelectron blocking layer, a hole injection layer and a hole transportinglayer doped with a p-dopant.

A second hole transporting layer may be positioned on the green emissionlayer in the blue sub-pixel area.

The second hole transporting layer may include at least one of anelectron blocking layer, a hole injection layer and a hole transportinglayer doped with a p-dopant.

A thickness of each of the red emission layer, the green emission layerand the blue emission layer may be between 50 Å and 500 Å.

A total thickness of the plurality of organic material layers positionedbetween the first electrode and the second electrode may be less than orequal to 2000 Å in the at least one of the red sub-pixel area, the greensub-pixel area and the blue sub-pixel area, in which the distancebetween the first electrode and the second electrode is λ/2n (e.g., thethickness of the organic light emitting device can be smaller than ahuman red blood cell, small bacteria and some viruses).

In another embodiment of the present invention, a method of fabricatingan organic light emitting device includes forming a first electrode, ahole injection layer, a hole transporting layer and a red emission layereach corresponding to an entirety of a red sub-pixel area, a greensub-pixel area and a blue sub-pixel area on a substrate, forming a firsthole transporting layer on the red emission layer in the green sub-pixelarea, forming a green emission layer corresponding to the entirety ofthe red sub-pixel area, the green sub-pixel area and the blue sub-pixelarea, forming a second hole transporting layer on the green emissionlayer in the blue sub-pixel area, forming a blue emission layercorresponding to the entirety of the red sub-pixel area, the greensub-pixel area and the blue sub-pixel area, and forming an electrontransporting layer, a second electrode and a capping layer on the blueemission layer.

Forming each of the first hole transporting layer and the second holetransporting layer comprise forming at least one of an electron blockinglayer, a hole injection layer and a hole transporting layer doped with ap-dopant in each of the first hole transporting layer and the secondhole transporting layer.

In another aspect of the present invention, an apparatus comprises anOLED device having a red emission layer, a green emission layer, and ablue emission layer which are non-patterned and stacked as common layersconfigured such that a thickness of each of a hole transporting layer,the red emission layer, the green emission layer, and the blue emissionlayer is respectively less than those corresponding layers in aconventional OLED device having a red emission layer, a green emissionlayer, and a blue emission layer which are patterned.

The common layers may comprise a red sub-pixel area, a green sub-pixelarea and a blue sub-pixel area, and the OLED device may emit a red lightin the red sub-pixel area, a green light in the green sub-pixel area anda blue light in the blue sub-pixel area.

The red sub-pixel area of the OLED device may comprise the red emissionlayer, the green emission layer disposed on the red emission layer, andthe blue emission layer disposed on the green emission layer.

The green sub-pixel area of the OLED device may comprise the redemission layer, a first hole transporting layer disposed on the redemission layer, the green emission layer disposed on the first holetransporting layer, and the blue emission layer disposed on the greenemission layer.

The first hole transporting layer may comprise at least one of anelectron blocking layer, a hole injection layer and a hole transportinglayer doped with a p-dopant.

The blue sub-pixel area of the OLED device may comprise the red emissionlayer, the green emission layer disposed on the red emission layer, asecond hole transporting layer disposed on the green emission layer, andthe blue emission layer disposed on the second hole transporting layer.

The second hole transporting layer may comprise at least one of anelectron blocking layer, a hole injection layer and a hole transportinglayer doped with a p-dopant.

According to embodiments of the present invention, by forming a redemission layer, a green emission layer and a blue emission layer ascommon layers corresponding to the entirety a red sub-pixel area Rp,green sub-pixel area Gp and blue sub-pixel area Bp of an organic lightemitting device, the number of fine metal masks (FMMs) used to form theorganic emission layers can be reduced, and a manufacturing process canbe simplified.

In addition, emission efficiency of an organic light emitting device maybe improved by causing a red sub-pixel area Rp or at least one of thered sub-pixel area Rp, a green sub-pixel area Gp and a the bluesub-pixel area Bp to have a first-order optical distance.

Further, a driving voltage of an organic light emitting device may belowered by applying a first-order optical distance to at least onesub-pixel area. Thereby, power consumption of the organic light emittingdevice may be reduced.

It should be noted that effects of the present invention are not limitedto those described above and other effects of the present invention willbe apparent to those skilled in the art from the following descriptions.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are not intended to specify essentiallimitations recited in the claims. Therefore, the scope of the claims isnot restricted by the foregoing general description and the followingdetailed description of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 schematically illustrates the structure of an organic lightemitting device of the related art;

FIG. 2 schematically illustrates the structure of an organic lightemitting device according to an embodiment of the present invention;

FIGS. 3A to 3D are cross-sectional views schematically illustrating amethod of fabricating an organic light emitting device according to anembodiment of the present invention;

FIG. 4 illustrates an evaluation result of electro-optical properties ofan organic light emitting device according to an embodiment of thepresent invention; and

FIG. 5 illustrates an evaluation result for properties of a panelincluding an organic light emitting device according to an embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Advantages and features of the present invention and methods to achievethem will become apparent from the descriptions of embodiments hereinbelow with reference to the accompanying drawings. However, the presentinvention is not limited to embodiments disclosed herein but may beimplemented in various different forms. The embodiments are provided formaking the disclosure of the present invention thorough and for fullyconveying the scope of the present invention to those skilled in theart. It is to be noted that the scope of the present invention isdefined only by the claims.

The figures, dimensions, ratios, angles, numbers of elements given inthe drawings are merely illustrative and are not limiting. Likereference numerals denote like elements throughout the descriptions.Further, in describing the present invention, descriptions on well-knowntechnologies may be omitted in order not to obscure the gist of thepresent invention. It is to be noticed that the terms “comprising,”“having,” “including” and so on, used in the description and claims,should not be interpreted as being restricted to the means listedthereafter unless specifically stated otherwise. Where an indefinite ordefinite article is used when referring to a singular noun, e.g. “a,”“an,” “the,” this includes a plural of that noun unless specificallystated otherwise.

In describing elements, the elements are interpreted as including errormargins even without explicit statements. In describing positionalrelationships, such as “an element A on an element B,” “an element Aabove an element B,” “an element A below an element B” and “an element Anext to an element B,” another element C may be disposed between theelements A and B unless the term “directly” or “immediately” isexplicitly used.

The terms first, second, third and the like in the descriptions and inthe claims are used for distinguishing between similar elements and notnecessarily illustrating a sequential or chronological order. Theseterms are used to merely distinguish one element from another.Accordingly, as used herein, a first element may be a second elementwithin the technical idea of the present invention.

Features of various embodiments of the present invention may be combinedpartially or totally. As will be clearly appreciated by those skilled inthe art, technically various interactions and operations are possible.Various embodiments can be practiced individually or in combination.

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings.

FIG. 2 schematically illustrates the structure of an organic lightemitting device 200 according to an embodiment of the present invention.

Referring to FIG. 2, the organic light emitting device 200 includes afirst electrode 210 (anode) formed on a substrate on which a redsub-pixel area Rp, a green sub-pixel area Gp and a blue sub-pixel areaBp are defined, a hole injection layer (HIL) 215, a common holetransporting layer (common HTL) 220, a red emission layer (red EML) 225,a first hole transporting layer 230 (G-HTL), a green emission layer(green EML) 235, a second hole transporting layer 240 (B-HTL), a blueemission layer (blue EML) 245, an electron transporting layer (ETL) 250,a second electrode 255 (cathode), and a capping layer (CPL) 260.

In addition, an OLED display including the organic light emitting device200 can include a gate line, a data line, and a power line. The gateline and data line are disposed on the substrate to cross each other todefine each sub-pixel area, and the power line is disposed to extend inparallel with one of the gate line and the data line. A switching thinfilm transistor (TFT) connected to the gate line and a data line and adriving TFT connected to the switching TFT are disposed in eachsub-pixel area. The driving TFT is connected to the first electrode 210(anode).

The first electrode 210 may be disposed on the substrate to correspondto all the red, green and blue sub-pixel areas Rp, Gp and Bp which aredefined on the substrate. The first electrode 210 may be a reflectiveelectrode.

For example, the first electrode 210 may include a transparentconductive material layer formed of a material having a relatively highwork function, such as indium-tin-oxide (ITO), and a reflective materiallayer formed of a material such as silver (Ag) or an Ag alloy.

The HIL 215 is formed to correspond to all of the red, green and bluesub-pixel areas Rp, Gp and Bp and disposed on the first electrode 210.

The HIL 215 may be formed by adding a p-dopant to a materialconstituting the HTL 220. In this instance, the HIL 215 and the HTL 220may be formed in a continuous process performed by one processingequipment.

The HIL 215 serves to facilitate injection of holes. The HIL 215 may beformed of at least one selected from a group consisting of HATCN(1,4,5,8,9,11-hexaazatriphenylene-hexanitrile), CuPc (cupperphthalocyanine), PEDOT (poly(3,4)-ethylenedioxythiophene),PANI(polyaniline) and NPD (N,N-dinaphthyl-N,N′-diphenylbenzidine), butembodiments of the present invention are not limited thereto.

The common HTL 220 is formed to correspond to all of the red, green andblue sub-pixel areas Rp, Gp and Bp and disposed on the HIL 215.

The common HTL 220 serves to facilitate transport of holes. The commonHTL 220 may be formed of at least one selected from a group consistingof NPD (N,N-dinaphthyl-N,N′-diphenylbenzidine), TPD(N,N′-bis-(3-methylphenyl)-N,N′-bis-(phenyl)-benzidine), s-TAD andMTDATA (4,4′,4″-Tris(N-3-methylphenyl-N-phenyl-amino)-triphenylamine),but embodiments of the present invention are not limited thereto.

For the organic light emitting device 200, the red EML 225 is formed asa common layer corresponding to the entirety of the red, green and bluesub-pixel areas Rp, Gp and Bp and disposed on the common HTL 220.

The red EML 225 may contain a luminescent material emitting red light.The luminescent material may employ a phosphorescent material or afluorescent material.

More specifically, the red EML 225 may contain a host material, whichincludes CBP (carbazole biphenyl) or mCP (1,3-bis(carbazol-9-yl). Thered EML 225 may be formed of a phosphorescent material including adopant, which includes at least one selected from a group consisting ofPIQIr(acac)(bis(1-phenylisoquinoline) acetylacetonate iridium),PQIr(acac)(bis(1-phenylquinoline) acetylacetonate iridium),PQIr(tris(1-phenylquinoline)iridium) and PtOEP(octaethylporphyrinplatinum). Alternatively, the red EML 225 may be formed of a fluorescentmaterial including PBD:Eu(DBM)3(Phen) or Perylene, but embodiments ofthe present invention are not limited thereto.

The first hole transporting layer 230 included in the organic lightemitting device 200, is disposed on the red EML 225 and formed tocorrespond to the green sub-pixel area Gp.

The first hole transporting layer 230 may perform the function of thefirst HTL (G-HTL) formed in the green sub-pixel area Gp. The first holetransporting layer 230 may be formed in the green sub-pixel area Gp todefine an optical distance of a micro cavity.

The first hole transporting layer 230 serves to facilitate transport ofholes. The first hole transporting layer 230 may be formed of at leastone selected from a group consisting of NPD(N,N-dinaphthyl-N,N′-diphenylbenzidine), TPD(N,N′-bis-(3-methylphenyl)-N,N′-bis-(phenyl)-benzidine), s-TAD andMTDATA (4,4′,4″-Tris(N-3-methylphenyl-N-phenyl-amino)-triphenylamine),but embodiments of the present invention are not limited thereto.

The first hole transporting layer 230 may include at least one of anelectron blocking layer (EBL), the HIL 215 and the HTL 220 doped with ap-dopant.

The EBL, not shown, functions to enhance emission efficiency of theorganic light emitting device by preventing electrons from flowing overto the HTL 220 such that holes are smoothly recombined with theelectrons in the organic emission layers.

The first hole transporting layer 230 including the EBL may blockelectrons from being transferred from the second electrode 255 to thered EML 225, thereby ensuring that desired light can be emitted from thegreen EML 235 in the green sub-pixel area Gp (e.g., blocking electronsfrom combining with holes in the red EML 222). For example, the greensub-pixel area can emit only green light while not emitting blue lightand not emitting red light.

The first hole transporting layer 230 including the HIL 215 or the HTL220 doped with the p-dopant may inject holes into the green EML 235adjacent thereto, thereby causing desired light to be emitted from thegreen EML 235 in the green sub-pixel area Gp.

The green EML 235 included in the organic light emitting device 200 isformed as a common layer corresponding to the entirety of the red, greenand blue sub-pixel areas Rp, Gp and Bp and disposed on the red EML 225and the first hole transporting layer 230.

The green EML 235 may contain a luminescent material emitting greenlight. The luminescent material may employ a phosphorescent material ora fluorescent material.

The green EML 235 may contain a host material including CBP or mCP. Thegreen EML 235 may be formed of a phosphorescent material including adopant material such as Ir complex including Ir(ppy)3(factris(2-phenylpyridine)iridium). Alternatively, the green EML 235 may beformed of a fluorescent material includingAlq3(tris(8-hydroxyquinolino)aluminum), but embodiments of the presentinvention are not limited thereto.

The second hole transporting layer 240 included in the organic lightemitting device 200 is disposed on the green EML 235 and formed tocorrespond to the blue sub-pixel area Bp.

The second hole transporting layer 240 may perform the function of thesecond HTL (B-HTL) formed in the blue sub-pixel area Bp, The second holetransporting layer 240 may be formed in the blue sub-pixel area Bp todefine an optical distance of a micro cavity.

The second hole transporting layer 240 serves to facilitate thetransport of holes. The second hole transporting layer 240 may be formedof at least one selected from a group consisting of NPD(N,N-dinaphthyl-N,N′-diphenylbenzidine), TPD(N,N′-bis-(3-methylphenyl)-N,N′-bis-(phenyl)-benzidine), s-TAD andMTDATA (4,4′,4″-Tris(N-3-methylphenyl-N-phenyl-amino)-triphenylamine),but embodiments of the present invention are not limited thereto.

The second hole transporting layer 240 may include at least one of aEBL, the HIL 215 and the HTL 220 doped with a p-dopant.

The second hole transporting layer 240 including the EBL may blockelectrons from being transferred from the second electrode 255 to thered EML 225 and the green EML 235, thereby ensuring that desired lightcan be emitted from the blue EML 245 in the blue sub-pixel area Bp(e.g., electrons and holes can only combine within the blue EML 245while only holes pass through the red EML 225 and the green EML 235).For example, the blue sub-pixel area can emit only blue light while notemitting green light and not emitting red light.

The second hole transporting layer 240 including the HIL 215 or the HTL220 doped with the p-dopant may inject holes into the blue EML 245adjacent thereto, thereby causing desired light to be emitted from theblue EML 245 in the blue sub-pixel area Bp.

The blue EML 245 included in the organic light emitting device 200 isformed as a common layer corresponding to the entirety of the red, greenand blue sub-pixel areas Rp, Gp and Bp, and disposed on the green EML235 and the second hole transporting layer 240.

The blue EML 245 may contain a luminescent material emitting blue light.The luminescent material may employ a phosphorescent material or afluorescent material.

The blue EML 245 may contain a host material including CBP or mCP. Theblue EML 245 may be formed of a phosphorescent material including adopant material including (4,6-F2ppy)2Irpic. Alternatively, the blue EML245 may be formed of a fluorescent material a fluorescent materialincluding at least one selected from a group consisting of Spiro-DPVBi,spiro-6P, distyrylbenzene (DSB), distyrylarylene (DSA), a PFO-basedpolymer and a PPV-based polymer, but embodiments of the presentinvention are not limited thereto.

In an embodiment of the invention, the green emission layer is disposedon the red emission layer, and the blue emission layer is disposed onthe green emission layer in each of the sub-pixel areas, and even thougheach sub-pixel area includes the red, green and blue emission layers,only red light can emit in the red sub-pixel area, only green light canemit in the green sub-pixel area and only blue light can emit in theblue sub-pixel area. For example, the red sub-pixel area can emit onlyred light while not emitting green and not emitting blue light, thegreen sub-pixel area can emit only green light while not emitting redlight and not emitting blue light, and the blue sub-pixel area can emitonly blue light while not emitting green light and not emitting redlight.

The ETL 250 is formed to correspond to all of the red, green and bluesub-pixel areas Rp, Gp and Bp and is disposed on the blue EML 245.

The ETL 250 may serve to transport and inject electrons. The thicknessof the ETL 250 may be adjusted in consideration of an electron transportproperty.

The ETL 250 functions to facilitate transport of electrons. The ETL 250may be formed of at least one selected from a group consisting ofAlq3(tris(8-hydroxyquinolino)aluminum),PBD(2-(4-biphenylyl)-5-(4-tert-butylpheny)-1,3,4oxadiazole), TAZ,Spiro-PBD, BAlq and SAlq, but embodiments of the present invention arenot limited thereto.

A separate electron injection layer (EIL), not shown, may be added tothe ETL 250.

The EIL may employ Alq3(tris(8-hydroxyquinolino)aluminum),PBD(2-(4-biphenylyl)-5-(4-tert-butylpheny)-1,3,4oxadiazole), TAZ,Spiro-PBD, BAlq or SAlq, but embodiments of the present invention arenot limited thereto.

Herein, the structure is not limited according to embodiments of thepresent invention. At least one of the HIL 215, the HTL 220, the ETL 250and the EIL may be omitted. In addition, any one of the HIL 215, the HTL220, the ETL 250 and the EIL may include two or more layers.

The second electrode 255 is disposed on the ETL 250. The secondelectrode 255 may be formed of, for example, an alloy (Mg:Ag) ofmagnesium (Mg) and silver (Ag) and thus may have a semi-transparentproperty. That is, light emitted from the organic emission layer isexternally displayed through the second electrode 255, and a part of thelight returns to the first electrode 210 since the second electrode 255has the semi-transparent property.

As such, repeated reflection occurs between the first electrode 210 andthe second electrode 255 acting as reflective layers, which is called amicro cavity effect (e.g., an optical resonator for particularwavelengths). As light is repeatedly reflected in the cavity between thefirst electrode 210 and the second electrode 255, light emissionefficiency increases.

Alternatively, the first electrode 210 may be formed as a transmissiveelectrode, and the second electrode 255 may be formed as a reflectiveelectrode, such that light emitted from the organic emission layer isexternally displayed through the first electrode 210.

The CPL 260 is disposed on the second electrode 255. The CPL 260 isintended to boost the light extraction effect of the organic lightemitting device 200. The CPL 260 may be formed of one of the materialsof the HTL 220 and the ETL 250 and the host materials of the red EML225, the green EML 235 and the blue EML 245. Alternatively, the CPL 260may be omitted.

Regarding the organic light emitting device structure, in order toproduce the micro cavity effect with light of different wavelengthsgenerated in the respective sub-pixel areas constituting one pixel, thecavity length or depth of the organic light emitting device generatingdifferent emission wavelengths may become a multiple of the wavelengthof each emitted light. In this instance, emission efficiency may beimproved as the generated light is amplified within the micro cavitylength.

To obtain the micro cavity effect as above, a condition of mλ=2nd issatisfied. In other words, to obtain the micro cavity effect, thedistance between the first electrode and the second electrode, namelythe micro cavity length d is set to an integer multiple m of λ/2n.Herein, m denotes an order, λ denotes the wavelength of light emittedfrom each sub-pixel area, n denotes an average refractive index of aplurality of organic material layers disposed between the firstelectrode and the second electrode in each sub-pixel area, and d denotesa distance between the first electrode and the second electrode, namelya micro cavity length. The plurality of organic material layers disposedbetween the first electrode and the second electrode may include an HIL,an HTL, an organic EML, an ETL, and an EIL, but embodiments of thepresent invention are not limited thereto.

When the micro cavity length d is equal to the wavelength of the emittedlight (i.e., m=1), the organic light emitting device is called anorganic light emitting device having a first-order optical distance.When the micro cavity length d is twice the wavelength of the emittedlight (i.e., m=2), the organic light emitting device is called anorganic light emitting device having a second-order optical distance.

The organic light emitting device 100 illustrated in FIG. 1 includes thered EML 135, the green EML 140 and the blue EML 145 disposedrespectively in the red sub-pixel area Rp, the green sub-pixel area Gpand the blue sub-pixel area Bp between the first electrode 110 and thesecond electrode 155. The organic light emitting device 100 isstructured to have a second-order optical distance d between the firstelectrode 110 and the second electrode 155 in all the sub-pixel areas.That is, the second-order optical distance d is twice the wavelength ofemitted light (i.e., m=2), namely λ/n.

In other words, efficiency of the organic light emitting device 100 maybe improved by achieving the micro cavity by adjusting the thicknessesof the first and second hole transporting layers 125 and 130 and theorganic EMLs 135, 140 and 145. However, in this instance, as structureshaving a second-order distance are applied to all of the red, green, andblue sub-pixel areas Rp, Gp and Bp, the red EML 135 in the red sub-pixelarea Rp becomes thicker than the green EML 140 in the green sub-pixelarea Gp and the blue EML 145 in the blue sub-pixel area Bp.

As the red EML 135 in the red sub-pixel area Rp is formed to berelatively thick, the driving voltage of the organic light emittingdevice 100 significantly increases along with an increase in powerconsumption.

Further, as the red EML 135 becomes relatively thick, an opening of amask is clogged by organic materials in the deposition process of thethick organic emission layer. This phenomenon is called mask rib. Themask rib leads to a poor organic light emitting device.

Compared to the structure of the organic light emitting device 100 ofthe related art, the organic light emitting device 200 may be formed tohave a first-order optical distance in the red sub-pixel area Rp byreducing the thicknesses of the HTL 220 and the red EML 225.

According to one embodiment of the present invention, in order to ensurethat the organic light emitting device 200 has a first-order opticaldistance in the red sub-pixel area Rp, the HTL 220 may be formed suchthat the thickness is less than or equal to 1200 Å.

According to one embodiment of the present invention, the totalthickness of a plurality of organic material layers disposed between thefirst electrode 210 and the second electrode 255 may be less than orequal to 2000 Å in the red sub-pixel area Rp in which the organic lightemitting device 200 has a first-order optical distance. The plurality oforganic material layers disposed between the first electrode 210 and thesecond electrode 255 may include an HIL, an HTL, an organic EML, an ETLand an EIL, but embodiments of the present invention are limitedthereto.

Each of the red EML 225, the green EML 235 and the blue EML 245 may beformed to have a thickness within a range of 50 Å to 500 Å such that theorganic light emitting device 200 has a first-order optical distance inthe red sub-pixel area Rp.

While the organic light emitting device has been described as having afirst-order optical distance in the red sub-pixel area Rp, embodimentsof the present invention are not limited thereto. The organic lightemitting device may have a first-order optical distance in at least oneof the red, green and blue sub-pixel areas Rp, Gp and Bp, and the totalthickness of a plurality of organic material layers disposed between thefirst electrode 210 and the second electrode 255 may be less than orequal to 2000 Å in the at least one sub-pixel area in which thefirst-order optical distance is defined.

That is, the organic light emitting device 200 is structured to have afirst-order optical distance d between the first electrode 210 and thesecond electrode 255 in the red sub-pixel area Rp which is equal to thewavelength of the emitted light (i.e., m=1), namely λ/2n.

As the organic light emitting device 200 is structured to have afirst-order optical distance in the red sub-pixel area Rp, emissionefficiency of the organic light emitting device 200 may be improved forred light, compared to the emission efficiency of the organic lightemitting device 100 of the related art.

In addition, as the thicknesses of the HTL 220 and the red EML 225 arereduced to define the first-order optical distance in the red sub-pixelarea Rp, the organic light emitting device may be driven with a lowerdriving voltage, and power consumption in the organic light emittingdevice may be reduced.

Further, reducing the thickness of the red EML 225 may prevent a poororganic light emitting device from being produced by the mask rib, whichrefers to clogging of an opening of a mask caused by organic matter whena thick organic EML is deposited.

FIGS. 3A to 3D are cross-sectional views schematically illustrating amethod of fabricating the organic light emitting device 200 describedabove with reference to FIG. 2.

Hereinafter, a method of fabricating the organic light emitting device200 will be described in detail with reference to FIGS. 3A to 3D.

Referring to FIG. 3A, a first electrode 210, an HIL 215, an common HTL220 and a red EML 225 are formed to correspond to the entirety of a redsub-pixel area Rp, a green sub-pixel area Gp and a blue sub-pixel areaBp, which are defined on a substrate.

Next, referring to FIG. 3B, the first hole transporting layer 230 isformed on the red EML 225 in the green sub-pixel area Gp.

Next, a green EML 235 is formed on the red EML 225 and the first holetransporting layer 230 to correspond to the entirety of the red, greenand blue sub-pixel areas Rp, Gp and Bp.

Next, referring to FIG. 3C, a second hole transporting layer 240 isformed on the green EML 235 in the blue sub-pixel area Bp.

Next, a blue EML 245 is formed on the green EML 235 and the second holetransporting layer 240 to correspond to the entirety of the red, greenand blue sub-pixel areas Rp, Gp and Bp.

Next, referring to FIG. 3D, an ETL 250, a second electrode 255 and a CPL260 are formed on the blue EML 245 to correspond to the red, green andblue sub-pixel areas Rp, Gp and Bp.

With a fabrication method according to the structure of the organiclight emitting device 100, FMMs are needed to form first holetransporting layer 125, second hole transporting layer 130, red EML 135,green EML 140 and blue EML 145. Thereby, use of five FMMs is required.

With the fabrication method according to the structure of the organiclight emitting device 200, the red EML 225, the green EML 235 and theblue EML 245 are formed as common layers corresponding to the entiretyof the red, green and blue sub-pixel areas Rp, Gp and Bp, and thereforethey need no FMM. Thereby, an organic light emitting device can befabricated by using only two FMMs to form the first hole transportinglayer 230 and the second hole transporting layer 240.

In other words, as the red EML 225, the green EML 235 and the blue EML245 of the organic light emitting device 200 are formed as common layerscorresponding to the entirety of the red sub-pixel area Rp, the greensub-pixel area Gp and the blue sub-pixel area Bp, the number of masksused to form the organic EMLs can be reduced and the process offabricating the organic light emitting device can be simplified.

FIG. 4 illustrates an evaluation result of electro-optical properties ofthe organic light emitting device 200 according to an embodiment of thepresent invention.

In FIG. 4, the Comparative Example (related art) represents anevaluation result of electro-optical properties of the organic lightemitting device 100 described above with reference to FIG. 1.

And the Embodiment (present invention) represents an evaluation resultof electro-optical properties of the organic light emitting device 200described above with reference to FIG. 2.

FIG. 4 illustrates spectral intensities of red, green and blue lightemitted from organic light emitting devices according to the ComparativeExample and the Embodiment. For emission of the green and blue light,the intensities obtained in the Embodiment are not significantlydifferent from the intensity in the Comparative Example. For emission ofred light, the intensity obtained in the Comparative Example is 1,whereas the intensity in the Embodiment of the present invention is1.71. Therefore, it can be seen from FIG. 4 that the emission efficiencyof red light in the Embodiment about 1.7 times the emission efficiencyof red light in the Comparative Example.

Regarding color coordinates, FIG. 4 shows that the coordinates obtainedin the Embodiment are similar to those obtained in the ComparativeExample (e.g., CIE_x and CIE_y). Accordingly, it can be seen from FIG. 4that Embodiment satisfies desired color characteristics similar to thatof Comparative Example.

In other words, with the organic light emitting device 200, improvedemission efficiency of red light may be obtained by applying a structurehaving a first-order distance to the red sub-pixel area Rp.

FIG. 5 illustrates an evaluation result of panel properties of a panelincluding the organic light emitting device 200 according to anembodiment of the present invention.

In FIG. 5, the Comparative Example represents an evaluation result ofpanel properties of a panel including the organic light emitting device100 of the related art described above with reference to FIG. 1.

The Embodiment (present invention) shown in FIG. 5 represents anevaluation result of panel properties of a panel including the organiclight emitting device 200 described above with reference to FIG. 2.

Regarding driving voltages for red emission from the organic lightemitting device according to the Comparative Example and the Embodimentillustrated in FIG. 5, the Comparative Example requires about 5.1 V as adriving voltage for red emission, whereas the Embodiment requires about4.6 V as a driving voltage for red emission. Accordingly, the organiclight emitting device 200 can be driven by a driving voltage which isabout 0.5 V lower than the driving voltage of the Comparative Example.Thereby, reduction in driving voltage can be achieved with the organiclight emitting device 200.

Regarding emission efficiency of red light from OLED displays includingthe organic light emitting devices according to the Comparative Exampleand the Embodiment, FIG. 5 shows that the Comparative Example achievesan efficiency corresponding to 54.3 cd/A, and the Embodiment achieves anefficiency corresponding to 92.8 cd/A. Accordingly, the organic lightemitting device 200 may obtain an emission efficiency of red lightimproved by 38.5 cd/A from the efficiency obtained in the ComparativeExample.

Regarding power consumption in white emission from OLED displaysincluding the organic light emitting devices according to theComparative Example and the Embodiment, it can be seen from FIG. 5 thatthe Comparative Example requires power consumption of about 160 mW forwhite emission of a brightness level, whereas the Embodiment has a powerconsumption of 145 mW for white emission of the same brightness level.In other words, the Embodiment has a power consumption that is 10% lowerthan the power consumption of the Comparative Example. That is, an OLEDdisplay including the organic light emitting device 200 can be improvedin terms of power consumption.

According to an embodiment of the present invention, the red EML 225,the green EML 235 and the blue EML 245 of the organic light emittingdevice 200 may be formed as common layers each corresponding to theentirety of the red, green and blue sub-pixel areas Rp, Gp and Bp.Thereby, the number of FMMs used in forming organic EMLs may be reducedand the fabrication process may be simplified.

According to an embodiment of the present invention, the organic lightemitting device 200 may improve emission efficiency with a structurethat has a first-order optical distance applied to at least one of thered, green and blue sub-pixel areas Rp, Gp and Bp.

According to an embodiment of the present invention, with the organiclight emitting device 200, an OLED may be improved in terms of powerconsumption by reducing the driving voltage through application of astructure having a first-order optical distance.

Embodiments of the present invention have been described in detail abovewith reference to the accompanying drawings. Those skilled in the artwill appreciate that the present invention is not limited to theembodiments, and various modifications and variations can be made in thepresent invention without departing from the spirit or scope of theinvention. Accordingly, the embodiments described herein are merelyillustrative and are not intended to limit the scope of the presentinvention. The technical ideas of the present invention are not limitedby the embodiments. Therefore, the embodiments described herein shouldbe construed in all aspects as illustrative and not restrictive. Thescope of protection sought by the present invention should be determinedby the appended claims and their legal equivalents, and all changescoming within the meaning and equivalency range of the appended claimsare intended to be embraced therein.

What is claimed is:
 1. An organic light emitting device comprising: afirst electrode and a second electrode; a red emission layer, a greenemission layer and a blue emission layer positioned between the firstelectrode and the second electrode; a first hole transporting layerdisposed between the green emission layer and the red emission layer ina green sub-pixel area; and a second hole transporting layer disposedbetween the blue emission layer and the green emission layer in a bluesub-pixel area, an electron transporting layer, wherein each of the redemission layer, the green emission layer and the blue emission layer isdisposed in an entirety of a red sub-pixel area, the green sub-pixelarea and the blue sub-pixel area, wherein the green emission layer isdisposed between the blue emission layer and the red emission layer ineach of the red, green and blue sub-pixel areas, wherein a first side ofthe first hole transporting layer in the green sub-pixel area contactsside surfaces of the blue emission layer, the green emission layer andthe electron transporting layer in the red sub-pixel area, wherein asecond side of the first hole transporting layer in the green sub-pixelarea contacts side surfaces of the blue emission layer, the second holetransporting layer and the green emission layer in the blue sub-pixelarea, and wherein a distance between the first electrode and the secondelectrode in at least one of the red sub-pixel area, the green sub-pixelarea and the blue sub-pixel area is λ/2n, wherein λ is a wavelength oflight emitted from each of the sub-pixel areas, and n is an averagerefractive index of a plurality of organic material layers positionedbetween the first electrode and the second electrode.
 2. The organiclight emitting device of claim 1, wherein a red light emits in the redsub-pixel area, a green light emits in the green sub-pixel area and ablue light emits in the blue sub-pixel area.
 3. The organic lightemitting device of claim 1, further comprising a common holetransporting layer disposed in an entirety of the red sub-pixel area,green sub-pixel area and blue sub-pixel area and positioned below thered emission layer, the green emission layer and the blue emissionlayer, wherein a thickness of the common hole transporting layer isequal to or less than 1200 Å.
 4. The organic light emitting device ofclaim 1, wherein the distance between the first electrode and the secondelectrode in the red sub-pixel area is λ/2n, wherein λ is the wavelengthof light emitted from the red sub-pixel area, and n is the averagerefractive index of the plurality of organic material layers disposedbetween the first electrode and the second electrode in the redsub-pixel area.
 5. The organic light emitting device of claim 1, whereinthe first hole transporting layer comprises at least one of an electronblocking layer, a hole injection layer and a hole transporting layerdoped with a p-dopant.
 6. The organic light emitting device of claim 1,wherein the second hole transporting layer comprises at least one of anelectron blocking layer, a hole injection layer and a hole transportinglayer doped with a p-dopant.
 7. The organic light emitting device ofclaim 1, wherein a thickness of each of the red emission layer, thegreen emission layer and the blue emission layer is between 50 Å and 500Å.
 8. The organic light emitting device of claim 1, wherein a totalthickness of the plurality of organic material layers positioned betweenthe first electrode and the second electrode is equal to or less than2000 Å in the at least one of the red sub-pixel area, the greensub-pixel area and the blue sub-pixel area in which the distance betweenthe first electrode and the second electrode is λ/2n.
 9. The organiclight emitting device of claim 1, wherein a distance between the secondelectrode in the blue sub-pixel area and the first electrode is greaterthan a distance between the second electrode in the red sub-pixel areaand the first electrode, and wherein a distance between the secondelectrode in the blue sub-pixel area and the first electrode is lessthan a distance between the second electrode in the green sub-pixel areaand the first electrode.
 10. The organic light emitting device of claim1, wherein an upper surface of the green emission layer contacts a lowersurface of the blue emission layer in the red sub-pixel area, and alower surface of the green emission layer contacts an upper surface ofthe red emission layer in the red sub-pixel area, wherein an uppersurface of the green emission layer contacts a lower surface of the blueemission layer in the green sub-pixel area, and a lower surface of thefirst hole transporting layer contacts an upper surface of the redemission layer in the green sub-pixel area, and wherein an upper surfaceof the green emission layer contacts a lower surface of the second holetransporting layer in the blue sub-pixel area, and a lower surface ofthe green emission layer contacts an upper surface of the red emissionlayer in the blue sub-pixel area.